I’m keeping an open mind about the convertible puzzle, but in looking into the individual pieces, some additional points should be pointed out. First, I assume that the Tucker body in the September 9, 1950 LIFE archive
is body #57. It’s possible that Alex Tremulis got the body number wrong, but probably not.
If you take a closer look into the interior shot of #57, you get a better look at the “C” pillars in the plant:

A closeup shows that the pillar is marked “11” on the side facing the center of the plant:

Looking into the other photos of the wooden buck and especially the side view of the clay models, you can see a pillar is marked “9”:

This sideview from Design and Destiny shows #10 and #11 clearly:

At first I thought that #57 was just nearby the area where Tremulis helped build the “Tin Goose”, but now it’s clear that #57 is sitting in precisely the exact same location at which the “Tin Goose” was painstakingly crafted three years earlier.
The pillars in the plant were apparently marked with not only “A”, “B”, “C”, and “D” (with B and C pillars in the center of the building), but also numbered 1 through 20-something. This grid puts the clay models for the “Tin Goose” exactly between the B10 and C10 pillars. The LIFE photo shows #57 from the opposite view, one pillar past (less than) the 11 pillars, or right between the B10 and C10 pillars, which is exactly where you’d expect Tremulis to be working on the Tucker ’49 modifications – on the same hallowed grounds of the birth of the “Tin Goose”.
So, putting it together,
#57 is to the Tucker ‘49 as the “Tin Goose” is to the Tucker ’48. As much as I like convertibles, I think I’d have to agree with Randy Earle that not only should #57 be the coupe version with the big back window and modified front fenders (more on this later), but if it was restored back to its 1950 (actually 1948/49) configuration, you would still have THE ONLY, one-of-one, documented (thanks to LIFE) prototype 1949 Tucker in existence. That should/would push its value right up to #1038 (assuming a first-class restoration, which would be well-justified in this case).
I’m keeping an open mind, though, about the convertible. I suppose it is possible that
a frame went to Lencki prior to the shutdown, and that it was modified/strengthened to be a convertible. And that the convertible we see today may have been made with that frame and the miscellaneous #57 parts (hood, fenders, etc.) that ended up on that frame. It would have made everyone’s lives a lot easier, but so much less dramatic, had the convertible had
anything other than #57 as the claimed base. It would be devastatingly sad to think that #57 was cut up after the fact.
As an aside, below is Joe Lencki sitting in the Preston Tucker – Joe Lencki “Lencki Partner Special” at Indianapolis in 1947. Photo is from a great site, the Nevada Vintage Race Museum in Henderson, Nevada.

Anyway, I would hope that the intact #57 body and frame we see in the LIFE archives is still squirreled away in someone’s garage or barn, still waiting to be brought back to life (no pun intended) just as it was on September 9, 1950.